Reducing NOx emissions by DeNOx catalysis with storage/destorage constitutes one of the technical solutions for satisfying standards relating to this type of exhaust, in particular, the EURO IV standards.
To this end, use of a NOx trap, constituted of barium sulfate, for example, has been envisaged for absorbing NOx during standard operation of the engine.
When the trap becomes saturated, it is proposed to trigger a transient destorage stage by causing the engine to switch temporarily from its standard operating mode with a lean mixture to operating in a regeneration mode using a rich mixture. This produces reducing agents, such as HC and CO, for example, that enable the NOx to be reduced, which is then desorbed from the trap, as in a traditional catalytic unit.
For this purpose, such a system for providing assistance in regeneration includes means for controlling the operation of means for injecting fuel into the cylinders of the engine in order to cause the engine to switch from a standard mode of operation with a lean mixture to a regeneration mode of operation with a rich mixture.
One of the ways of knowing when the NOx trap is in a saturated state is to use a NOx sensor in the exhaust system.
However, present NOx sensors are unreliable and relatively expensive.